1. Field of the Invention
The invention relates to a process and a device for adjusting the distance between a workpiece and a mask in an exposure device which is used in the process of manufacturing a semiconductor device.
2. Description of Related Art
Conventionally, so-called proximity exposure is done in which a workpiece and a mask are arranged at microscopically small distance to one another. In doing so, a semiconductor wafer or a glass substrate for a liquid crystal display is used for a workpiece. In the following, a workpiece is representatively called a wafer.
FIG. 12 schematically shows a proximity exposure device. Emitted light from light source 1 is incident by means of oval reflector 2 on integrator lens 3. Output light from integrator lens 3, after one passage through collimation lens 4, passes through mask M, on which a circuit pattern and the like are drawn, and irradiates wafer W. A distance between mask M and wafer W is roughly 20 microns, with a tolerance of no more than 2 microns.
The aforementioned "microscopic distance" was usually attained in such a way that a carrier with a spherical seat system is moved up and down relative to the mask M. FIG. 11 shows a device using such a spherical seat system.
Carrier 5 on which a wafer W is placed is located on spherical seat Carrier 5 is provided with vacuum line 8 for drawing the wafer onto carrier 5 by suction. Spherical seat 6 is provided with a vacuum line 9 for holding carrier 5 on the spherical seat 6. Vacuum lines 8 and 9 are connected to a vacuum suction holder which is not shown in the drawing. Spherical seat 6 can be moved up and down by means a moving device 7. In a device of this type, the processes described below are executed:
First, carrier 5 is lowered sufficiently by means of the moving device 7. In this state wafer W is seated on carrier 5. Then, wafer W is drawn against carrier 5 by operation of the vacuum suction holder and vacuum line 8. While the wafer W is held against the carrier 5, it is raised in the direction toward mask M by the moving device 7. In this case, the vacuum line 9 is not yet activated and spherical seat 6 and carrier 5 are arranged in a free positional relationship to one another.
After raising wafer W until it comes into contact with mask M, moving device 7, and thus upwards motion of wafer W, are stopped. Carrier 5 is tilted in this case by means of spherical seat 6, so that it is located parallel to mask M. In this way, a parallel positional relationship between wafer W and mask M is achieved.
Next, carrier 5 is drawn by suction onto spherical seat 6 by activating vacuum line 9. Then, carrier 5 is lowered by only a set distance. This distance is the above-mentioned "microscopic distance".
Distance adjustment of this type between the wafer and a mask must be done each time when a wafer is exposed. This is because when wafer W is drawn onto carrier 5 by suction, as the result of the nonuniformity of the suction, wafer W is tilted, or that as the result of the nonuniform thickness of the respective wafer W a deviation of the parallel positional relationship occurs between wafer W and mask M.
In the process described above for adjusting the distance between a mask and a wafer using a spherical seat system, it is considered a disadvantage that high surface precision of the spherical surface is required and that, therefore, producing the carrier and the spherical seat is both time- and cost-intensive.